Influenza virus activity in the world

28 September 2012

Source: Laboratory confirmed data from the Global Influenza Surveillance and Response System (GISRS).

Based on FluNet reporting (as of 25 September 2012, 11:00 UTC), during weeks 36 to 37 (2 to 15 September 2012), National Influenza Centres (NICs) and other national influenza laboratories from 75 countries, areas or territories reported data. The WHO GISRS laboratories tested more than 17 228 specimens. 1 501 were positive for influenza viruses, of which 968 (64.5%) were typed as influenza A and 533 (35.5%) as influenza B. Of the subtyped seasonal influenza A viruses, 161 (20.5%) were influenza A(H1N1)pdm09 and 624 (79.5%) were influenza A(H3N2). Of the characterized B viruses, 6 (50%) belong to the B-Yamagata lineage and 6 (50%) to the B-Victoria lineage. In addition, 7 detections of A(H3N2)v viruses were reported from the United States of America.

Summary

During weeks 36 and 37, influenza activity in general remained low in the southern hemisphere. Globally, influenza A(H3N2) viruses remained the predominant subtype followed by influenza B and A(H1N1)pdm09 viruses.

Influenza virus detections decreased in Australia and New Zealand with A(H3N2) and influenza B viruses co-circulating.

In Africa, influenza B activity remained high in South Africa, while in eastern and western Africa, sporadic activity of A(H1N1)pdm09, A(H3N2) and B viruses was reported.

In Asia, increased activity of influenza A(H1N1)pdm09 and B viruses was reported in Nepal. Local outbreaks of influenza A(H1N1)pdm09 and B continued in India and local outbreaks of A(H3N2) continued in Japan.

Influenza activity in Central and South America remained low. At low levels, influenza A(H3N2) and B viruses co-circulated in Central America. In Argentina, the number of influenza A(H1N1)pdm09 viruses detected increased slightly. Sporadic detections of influenza were reported from elsewhere in the region.

Influenza activity remained low in Europe and North America.

To date, 305 laboratory confirmed cases of infection with (H3N2)v viruses have been detected in the United States of America with 1 death and 16 hospitalizations reported.

Following the WHO Consultation on the Composition of Influenza Virus Vaccines for the Southern Hemisphere 2013, from 17 to 19 September 2012, it was recommended that the influenza vaccines for the southern hemisphere 2013 season contain the following viruses:

For the trivalent vaccine:

an A/California/7/2009 (H1N1)pdm09-like virus;

an A/Victoria/361/2011 (H3N2)-like virus;

a B/Wisconsin/1/2010-like virus;

This is the same composition as that recommended by WHO for the vaccine for the northern hemisphere 2012-2013 season.

For the quadrivalent vaccine containing two B viruses, it is recommended to include the above three viruses and a B/Brisbane/60/2008-like virus.